This invention relates to a method and an apparatus for desulfurization and denitrification of waste gas by electron beam irradiation.
A technique has heretofore been developed, where with radiating electron beam to various waste gas containing nitrogen exides (NOx) and/or sulfur dioxide (SO.sub.2), a small quantity of ammonia is added to the waste gas before, during or after the irradiation to make the ammonia react with NOx and SO.sub.2 so that poisonous gas component is converted into an aerosol, which is then removed by a dust collector, an improved method of the technique has further been studied.
A typical flow sheet and apparatus of commercial plant to which said method is applied are illustrated in FIG. 1. The apparatus comprises a device for supplying ammonia (1), a single stage of irradiating unit (4) which has an irradiating reaction vessel (2) and generator for electron beam (3) as its main elements, and aerosol collecting device (5) for aerosol separation which is formed in the waste gas by irradiation. These devices are connected in series along a stream of the waste gas.
The data in FIG. 2 was obtained by irradiating waste gas with electron beams by use of the conventional apparatus comprising said devices. FIG. 2 shows the relative relationships between the absorbed dose by the waste gas, and each of desulfurization and denitrification efficiencies.
As will be apparent from FIG. 2, both efficiencies have a tendency to increase greatly with increasing absorbed dose at the beginning, and then the efficiencies increase more slowly by degrees. Particularly the denitrification efficiencies decrease after a maximum point of 90%, namely the relationship between denitrification efficiencies and the absorbed dose is roughly linear in the region where the absorbed dose is relatively small, not more than 1 Mrad, while in the region of more than 1 Mrad, the denitrification efficiencies decrease.
Therefore, as will be apparent from FIG. 2, for example in the case that more than 80% of the dentitrification efficiencies are required, the denitrification process is to be operated under uneconomical high dose condition and resulting efficiencies cannot reach more than 90%.
As a result of studies to develop a method and apparatus for treatment of a waste gas by which the aforementioned defect is corrected and economical operation with from 90-100% of denitrification efficiencies is possible, the inventors of this invention have succeeded in developing a novel and useful technique.